The present invention relates to a method for preserving food products using an antimicrobial system. More particularly, the invention relates to the use of an antimicrobial system containing acetic acid and/or salt of acetic acid effective for controlling growth of spoilage and/or pathogenic bacteria in chilled foods and beverages.
Food can be unsafe to eat or drink, for many reasons. It can contain toxins or viruses, and even parasitic protozoa and worms. More frequently in Western countries, food is subjected to pathogenic bacteria poisoning.
For instance, Escherichia coli has been known for years to cause diarrhoea in infants, and gastro-enteritis in humans, associated with abdominal cramps, low-grade fever, nausea and malaise. Escherichia coli can be found in water, leading to food contamination. It is frequently isolated from dairy products, such as Semi-soft cheeses, for example.
Salmonella spp. are Gram-negative bacteria widespread in poultry and swine, but the environmental sources of these organisms also include water, soil, insects, factory or kitchen surfaces, raw meats and seafoods, etc. They are responsible for acute symptoms, but are also frequently associated with chronic consequences such as arthritic symptoms.
Bacillus cereus is a Gram-positive bacterium incriminated in a wide variety of foods including meats, milk, vegetables, fish, and starchy foods. It causes diarrhoea, abdominal cramps, pain and nausea.
Listeria monocytogenes is particularly dangerous to pregnant women and elderly people. The manifestations of this Gram-positive bacterium include septicaemia, meningitis, encephalitis, or intrauterine or cervical infections it pregnant women. This bacterium may be found in foods such as raw milk, cheeses, ice cream, raw vegetables, raw meats, fermented raw-meat sausages, etc. Its ability to grow at temperatures as low as 3xc2x0 C. permits multiplication in refrigerated foods.
Commercial acetic acid, acetates, and more specifically sodium acetate, as produced from gas or oil, are known as having antimicrobial properties against many foodborne pathogens, especially against Salmonella spp and Escherichia coli, particularly when used in combination with primary hurdles such as temperature and/or high acidity. However, these compounds are less effective when they are used as a primary hurdle against microorganisms such as Listeria monocytogenes, lactic acid bacteria, yeast and molds.
The preservative properties of acetic acid and salts of acetic acid in foods are described in the literature. In particular, U.S. Pat. No. 5,811,147 relates to a food and beverage preservative comprising a calcium component dissolved in a fermented solution of vinegar, alcohol, and a fermenting agent. The calcium component, coming mostly from shells or bones, is present in an amount of 3000 to 4000 mg, in 100 to 200 cc of the preservative solution. The preservative contains a relatively high concentration of alcohol (5 to 95%) as resulting from the process of producing the preservative, which has a positive effect on reduction of bacteria but may render the use of the preservative unsuitable for some food or beverage categories and, more specifically, as it may adversely affect the taste and flavor of the food product. Furthermore, the preservative composition contains calcium in amounts which increases the final cost of the food product. Furthermore, in certain circumstances, calcium-containing food may be not allowed for people having specific diseases such as hyperparathyroidies, kidney lithiasis, hypersensitivity to vitamin D or others.
U.S. Pat. No. 5,431,940 relates to a process for preparing noncarbonated beverage products with improved microbial stability which comprises mixing of a preservative (chosen from the group consisting of sorbic acid, benzoic acid, alkali metal salts thereof and mixtures thereof, fruit juice, polyphosphates and water. The process aims to control microbial growth in noncarbonated diluted juice beverages.
The methods of preservation of food of the prior art have restricted applications in the food and beverage domain, in particular, in the conditions of preservation of chilled products. Furthermore, none of the methods have proved to give a satisfactory inhibitory effect on pathogenic bacteria, in particular on Listeria monocytogenes, at chilled or abuse temperatures. The present invention proposes to overcome these problems, with the aim of obtaining a method of preservation usable for food and beverage, while controlling the growth of microorganisms capable of causing spoilage and/or pathogenic infection of the product.
The present invention provides an efficient and cost effective method for preserving food products from spoilage of microorganisms, for shelf life extension or pathogenic microorganisms, in particular, even if non-exclusively, Listeria monocytogenes, at chilled and chilled abuse temperatures. This method comprises adding to a food product an alcohol-free fermentate comprising of acetic acid and/or its salts resulting from the fermentation by acetic acid producing bacteria, and wherein the food is maintained at pH below 5.8.
It has been found that a fermentate of acetic acid or its salts used as a preservative system, by itself, as opposed to commercial or pure acetic acid or salt of acetic acid, had an improved inhibitory effect on Gram- negative and Gram-positive bacteria in food products during storage at chilled and chilled abuse conditions during the storage of the food product provided the acidity of the food product can be maintained at a sufficient level.
It has also been found that the inhibitory effect was even more remarkable at pH of about 5.6 or below, of the food product. The pH of the product has proved to be important for the fermentate to be fully effective. In particular, it is theorized that at lower pH, as defined, a sufficient amount of undissociated acetic acid compounds is formed in the food product which effects inhibition on the pathogenic microorganisms.
An inhibitory effect is also noticed particularly when the fermentate is added to the food product in an amount corresponding to a concentration of about 0.2 to 1% by weight of acetic acid and/or its salts, upon the weight of the food product. Preferably, the fermentate is added to the food product in an amount of from about 0.25 to 0.6 % by weight of acetic acid or its salts based upon the weight of the food product. A superior inhibitory effect is noticed at 0.5 (+/xe2x88x920.01) % by weight.
The method of the invention includes the step of producing a fermentate of acetic acid and/or salt of acetic acid from a bacterial growth medium inoculated with an acetic acid producing bacterium and sodium hydroxide so as to produce said acetic acid and/or salt of acetic acid at a controlled pH. A preferred pH of the medium is of from about 3.8 to 5.2, preferably of about 5. At such a pH level, the resulting fermentate, when transformed into a powder, has improved flowing properties. The medium preferably comprises at least one carbohydrate, alcohol, yeast extract, peptone and water.
Fermentation is preferably carried out for at least 2 days, preferably for about 5 to 10 days, even more preferably for 7 days, so as to reach an effective amount of growth of the acetic acid producing bacterium and of a suitable concentration of acetic acid and acetate in the fermentate. A suitable concentration of acetic acid and salt of acetic acid in the fermentate is about 3 to 6 g/L.
In a preferred aspect of the invention, the method further comprises the step of drying of the fermentate prior to its addition to the food product so as to produce a powdered preservative. Drying of the fermentate enables the reduction of the alcoholic compounds to infinitesimal and negligible concentrations, favors the stability of the preservative over time and facilitates the proper dosage of the preservative in the food product.